1. Field of the Invention
The present invention relates to a lens barrel for holding an optical lens element and a lens device comprising an optical lens element and a lens barrel.
2. Description of Related Art
In recent years because of a strong demand for a high optical performance and a decreased number of lens elements of a lens system for a liquid crystal projector, it is predominant to employ aspherical plastic lens elements. The problem encountered by such a plastic lens element is a higher expansion coefficient than glass lens elements and hardly adaptable to changes in environmental conditions such as ambient temperature and/or humidity. In consequence, the plastic lens element causes deterioration in lens performance resulting from a deviation of optical axis due to thermal expansion.
Japanese Unexamined Patent Publication No. 2000-187144 describes one of lens device structures for preventing a plastic lens and a lens barrel from having an adverse effect of expansion or contraction due to environmental changes such as temperature and humidity on each other. According the lens device structure, the lens device comprises a plastic lens element having a circumferential rim sure and a lens barrel fitted in the circumferential rim structure. This lens device is provided with a back k-lash between the circumferential rim structure and the lens barrel by which dimensional changes such as expansion and contraction of them due to changes in temperature and/or humidity are absorbed, so as thereby to retain initially attained axial concentricity for elimination of an adverse effect on optical performance of the lens device.
However, the optical lens element with a circumferential rim structure and the lens barrel to fit in the circumferential rim structure are not versatile in configuration and remain costly alternatives. It is conceivable to form an optical lens element and a lens barrel so as to leave a relatively wide clearance between a periphery of the optical lens element and the lens barrel for insertion of a separate ring-shaped retaining member in the clearance in order to retain the optical lens elements on the lens barrel. However, it goes counter to cost saving of the lens barrel, and besides leading to an increase in coaxial misalignment between the optical lens element and the lens barrel, to form the lens barrel so as to provide a clearance around a periphery of the optical lens element.